1. Field of the Invention
The present invention relates to a GPS/dead-reckoning combination system, and an operating method thereof.
2. Description of the Background Art
The LBS (Location Based Service) basically includes a GPS (Global Positioning System) receiver for computing an absolute position data and receiving a GPS data. A dead-reckoning system is additionally provided therein for generating a position data in the case that it is impossible to receive a GPS data. Here, the dead-reckoning system is capable of generating a position reckoning data using an inertia sensor (speed/angle sensor).
The GPS represents a global positioning system developed by the department of defense of the US and is capable of computing the position of a measuring person in a 3 D coordinate based on the measured data.
In a navigation system based on GPS, a GPS receiver is necessarily needed. Here, the GPS receiver is designed to receive signals from at least four satellites among 24 satellites flying in the space. In addition, a position vector of a GPS receiver is computed using a distance between a GPS satellite and a GPS receiver and a position vector of the GPS satellite. It is possible to compute the position of a receiver in a 3 D coordinate using the GPS receiver anywhere in the world.
It is possible to obtain a very accurate data using the GPS receiver, but the GPS is basically designed to receive signals only in a limited region in which a satellite signal can be received based on its basic measuring principle.
Namely, since the position of a receiver is computed using a GPS satellite, it is impossible to compute the position of a vehicle that uses a GPS receiver in a tunnel, a forest, a downtown surrounded by high buildings, etc. In addition, a result of position computation is not accurate.
In order to overcome the above problems that a position computation is impossible using a GPS satellite, a dead-reckoning system has been developed for thereby measuring a moving distance and a moving direction of a vehicle and estimating the current position of a vehicle.
The above dead-reckoning system needs a position value that could be used at an initial stage, and a moving distance and a moving direction must be continuously measured based on an initial position of a vehicle using an odometer having a revolution and angle change degree sensor and a gyroscope.
In addition, the dead-reckoning system continuously integrates a revolution and angle change degree based on a result of the measurement for thereby continuously computing the current position of a vehicle without any external assistance.
However, in the dead-reckoning system, an initial position data must be accurately set. In addition, when a vehicle runs for a long time period in a state that a position is estimated using a dead-reckoning system, the positions measured are inaccurate due to an accumulation of the measuring errors of each sensor.
For example, a position estimation must be continuously performed based on a dead-reckoning method in a region in which there is a long tunnel or a region surrounded by high mountains, so that an accumulation error is in proportion to time period.
In order to overcome the above problems, a navigation system has been developed wherein a gyroscope capable of computing a moving direction angle of a vehicle and an odometer capable of computing a moving distance are combined in a GPS. The above system is called a GPS/dead-reckoning combination system because it provides a reference position value needed for a dead-reckoning operation using a GPS receiver.
FIG. 1 is a view illustrating the construction of a related GPS/dead-reckoning combination system.
As shown therein, the related GPS/dead-reckoning combination system 100 includes a GPS receiver 101 capable of receiving an absolute position data of a certain moving unit. The related GPS/dead-reckoning system 100 includes an inertia sensor 102 capable of measuring a displacement of a moving unit, and a dead-reckoning processor 103 capable of measuring a running distance using the inertia sensor 102.
The GPS/dead-reckoning combination system 100 includes a Kalman filter 104 capable of estimating the current position of a certain moving unit using an absolute position data from the GPS receiver 101 and a running distance measured by the dead-reckoning processor 103.
The GPS/dead-reckoning combination system 100 estimates a new position using a moving direction angle and a moving distance measured by the inertia sensor 102 using a result of the position computation of the GPS receiver 101 in a region in which a GPS receiving is available, and a result of the GPS receiving position computation in the latest region.
FIG. 2 is a view for describing a problem occurring when a vehicle backwardly moves along a curved line in the related GPS/dead-reckoning combination system.
Here, a solid line represents a real path that a vehicle backwardly moves at an angle of α°, and a dotted line represents an estimated path that a vehicle forwardly moves at an angle of α° based on a dead-reckoning method. Therefore, according to the related GPS/dead-reckoning combination system, when position estimation is performed based on the dead-reckoning method, the current position of a vehicle is estimated assuming that the vehicle is forwardly moved even though the vehicle is actually backwardly moved.
The above problem occurs because a backward movement of a vehicle is not considered in a process algorithm in the related GPS/dead-reckoning combination system. Therefore, when a moving unit is backwardly moved, a position data error may occur in the related art.
FIG. 3 is a view for describing a problem that occurs when a vehicle is forwardly or backwardly moved in the related GPS/dead-reckoning combination system.
As shown therein, a solid line represents a real path that a vehicle is backwardly moved by L1, and is forwardly moved by L2, and is backwardly moved by L3, and a dotted line represents an estimated path that a vehicle is forwardly moved by L1, L2 and L3, respectively.
Therefore, assuming that there are no turn and backward movement, and there are only forward movement and backward movement, as the backward movement is repeatedly performed, the actual position of a moving unit may be largely different from the position estimated by the related GPS/dead-reckoning combination system.
In addition, when the position data is computed using the GPS/dead-reckoning combination system in the areas of high buildings, underground parking lot, and apartment parking lot and under a high level road, more critical error may occur in the position estimation as compared to a region in which the GPS receiving is available.
As a result, the errors occurring in the position estimation of a moving unit could be a very bad problem in the LBS system that needs a very accurate position data.